Light-transmitting metal oxides have been used in semiconductor devices. For example, conductive metal oxides (hereinafter referred to as oxide conductors) such as indium tin oxide (ITO) are used as materials for transparent electrodes that are necessary in display devices such as liquid crystal displays.
Moreover, light-transmitting metal oxides have attracted attention as materials having semiconductor properties. For example, In—Ga—Zn—O-based oxides and the like have been expected to be used as semiconductor materials that are necessary in display devices such as liquid crystal displays. In particular, they have been expected to be used for channel layers in thin film transistors (hereinafter also referred to as TFTs).
TFTs that include metal oxides having semiconductor properties (hereinafter such oxides are referred to as oxide semiconductors) can be formed by low-temperature processes. Thus, the oxide semiconductors have been increasingly expected to surpass or replace amorphous silicon used in display devices and the like.
The use of oxide conductors and oxide semiconductors that have light-transmitting properties enables the production of light-transmitting TFTs (e.g., see Reference 1).
Furthermore, a TFT including an oxide semiconductor as a channel layer has high field effect mobility. Therefore, a driver circuit in a display device or the like can be formed using such TFTs (e.g., see Reference 2).